A new relaxation pathway of optically allowed valence-excitations in molecules bound to metal atoms was investigated. We show that the σnonπ* excitation of HCN in MgnHCN (n = 1,2) clusters decays through the emission of an electron from the metallic component. The calculated lifetimes are of the order of 140 fs for MgHCN and 25 fs for Mg2HCN. These short lifetimes suggest that the relaxation mechanism discussed here should dominate for molecules adsorbed on metal clusters or surfaces. We find that at large distances this decay is dominated by energy transfer.